A Catholic fundamentalist who controls a network of right-wing groups funded by dark money has put three justices on the court. He’s about to get a fourth.

When President Donald Trump nominates a justice to the Supreme Court on Monday night, he will be carrying out the agenda of a small, secretive network of extremely conservative Catholic activists already responsible for placing three justices (Alito, Roberts, and Gorsuch) on the high court.

And yet few people know who they are—until now.

At the center of the network is Leonard Leo of the Federalist Society, the association of legal professionals that has been the pipeline for nearly all of Trump’s judicial nominees. (Leo is on leave from the Federalist Society to personally assist Trump in picking a replacement for Justice Anthony Kennedy.) His formal title is executive vice president, but that role belies Leo’s influence.

Directly or through surrogates, he has placed dozens of life-tenure judges on the federal bench; effectively controls the Judicial Crisis Network, which led the opposition to President Obama’s high court nominee, Judge Merrick Garland; he heavily influences the Becket Fund law firm that represented Hobby Lobby in its successful challenge of contraception; and now supervises admissions and hires at the George Mason Law School, newly renamed in memory of Justice Antonin Scalia.